Social Vigilance Behaviour of the Chacma Baboon, Papio Ursinus

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1. Observations of 3 groups of baboons having overlapping territories in the Cape of Good Hope Nature Reserve were carried out on 60 days during 1958/59. 2. Social vigilance behaviour of group and individual animals was recorded in detail when observers first encountered a group, when following a group, when a group was leaving or returning to its sleeping lairs, and when it was crossing a traffic-frequented road. Such situations, as judged from the behaviour of the groups, usually set up some degree of disturbance. 3. Results showed that: 1) single animals (usually young males) foraging ahead of a group might sometimes give the first warning of intruders. 2) females, closely associated with a large male, might maintain vigilance after the group, including the large male, had gone away. 3) large males were frequently very prominent both in stationary and in mobile vigilance behaviour, 'scanning', sitting and waiting till a group had passed ahead, and appearing very quickly to investigate after alarm barking by another animal. 4) higher-intensity vigilance by a large male was observed on different occasions, each of which involved an unusual potential threat-first presence of observers in the early morning close above the sleeping krantzes, losing visual contact with observers in swirling mist, and encroachment of a neighbouring group within or close to the territory. This type of vigilance had a two-fold effect in inhibiting normal activities of the group and in closing-up their formation. 5) a group tended to halt and wait when observers were met on its day-route; the waiting might last, in presumably hungry animals, for several hours, before a detour was initiated. 6) crossing a road showed prominent before and after vigilance by large males. 4. Assessment of all forms of social vigilance behaviour indicates that it comprises the following: 1) early warning given by a straying, restless, independent animal who is temporarily spatially remote from the main body = incidental vigilance 2) consistent watchfulness by large males, who may derive cues from the 'incidental' animals, and who may dominate and direct group behaviour in a situation perceived as threatening = dominant vigilance 3) miscellaneous barking by several animals, including young and females = undifferentiated vigilance. 5. Behaviour and social organization of baboon groups can only be objectively observed and described if presumptive terms such as 'sentinel', 'guardian', and 'leader', are discarded. A terminology consistent with the concepts of comparative and experimental behaviour study is required. 6. Comparison with data from other vertebrate groups, including 'lek' birds, ungulates, and a few species of monkey, provides some parallels in the vigilance functions of 'fringe' animals as well as of 'dominant' animals. 7. Although the present results are only a prelude to further extended study, they seem to indicate significant forms of social vigilance in baboons that are a by-product of the particular form of dominance-hierarchy and sexual-social relationships within the group. The generality of the findings must be checked by intensive field work on baboon groups in different environments.